The present disclosure relates generally to ram air turbines for aerospace applications. More particularly, this disclosure relates to an improved mounting system for a ram air turbine.
Aircrafts include, as standard equipment, a back-up power source for use in times of power outage in the main power system. This standard equipment generally includes a ram air turbine (RAT). The RAT is stowed in a storage bay within the fuselage or wing of an aircraft. Should the main power system of the aircraft go offline, the RAT can be deployed into the airstream surrounding the aircraft where the passing air relative to the speed of the aircraft causes the turbine blades of the RAT to rotate. The RAT may generate hydraulic power, electric power, or both. The RAT is coupled to suitable power generating equipment, such as a hydraulic pump for hydraulic power, or an electric generator for electric power, or both in the case of a hybrid RAT.
Both in the stowed position and especially in the deployed operating position of the RAT, the RAT can exhibit multiple resonance modes. These resonant modes can be damaging to the RAT and the support structure connecting the RAT to the aircraft if the resonant modes occur within 15% of the dynamic loading frequencies, such as in the case of turbine rotation frequency (commonly referred to as the operating range) of the RAT in the deployed position. For example, every RAT includes a torsion mode which can cause a turbine nose of the RAT to move from side to side and cause the support structure of the RAT to deform torsionally. A heel-toe mode is a resonance mode that can cause the turbine nose to move up and down and cause both the driveshaft of the turbine of the RAT and the support structure of the RAT to bend. In the stowed position, the RAT could be subjected to dynamic loading during a main engine fan-blade-out event. In this case, it is desirable for the RAT resonant modes to stay above engine wind milling upper limit by 15%.
The theory is known that substantially increasing the stiffness of the support structure of the RAT can move the harmonic frequency range at which these resonance modes of the RAT occur away from the frequencies of the operating range of the RAT. However, manufacturing a high stiffness aircraft mounting structure has been traditionally difficult to achieve, being both weight and cost prohibitive, and a RAT without a frame is more difficult to install in the aircraft.